Expulsion fuse and fuse link for use therein



G. F. LINC KS Inventor. George F: Lincks by His Attorneg.

July 28, 1942.

EXPULSION FUSE AND FUSE LINK FOR USE THEREIH Filed June '1, 1940 Fig. a.

V w M Patented July .28, 1942 UNITED STATES PATENT OFFICE 3,291,341 EXPULSION FUSE AND FUSE LINK ron use 'rnnnnm George F. Lincks, Pitt'sfield, Mass., assignor to General Electric Company, a corporation of New York Application June 7, 1940, Serial No. 339,297 Claims. (Cl. 200-135) The present invention relates to electric protective devices, more particularly expulsion fuses, and has for a general object the Provision of improvements whereby such fuses may be made to have increased pressure limits and greater capacity for interruption of excess currents of large magnitude, while at the same time being capable'of effectively interrupting excess cur- ,rents of small magnitude.

One of the more specific objects of the invention is the provision in an expulsion fuse, of inn-- proved construction and arrangement of parts for carrying out in a simple, practical, and economical manner the invention disclosed and broad 1y claimed in United States Patent No. 2,156,058, granted April 25, 1939, in the name of K. A. Lo hausen, and assigned to the assignee of the present invention.

As pointed out in the Lohausen patent, it has been found that for successful interruption of excess current of large magnitude, such as shortcircuit current, by means of an expulsion fuse, there is required not only a strong enclosing casing capable of withstanding the high pressures developed, but also a certain minimum and comparatively large cross-section of expulsion bore in order to prevent rise of the pressures beyond safe limits. On the other hand, it is required for satisfactory interruption of excess current of small magnitude, such as relatively small over load current, that the cross-section of expulsion bore be as small as possible in order that sufficient pressure may be developed for proper arc extinction.

signed so as to be capable of effecting interruption therein of arcs incident to excess current of small magnitude, while the partitions or walls of the compartments are designed to yield, upon development of high pressure incident to rupture of the fusible element by large magnitude excess current, so as to afford enlargement of the gas expansion space to a size corresponding substantially to the cross-sectional area of the main bore of the enclosing casing. The completely assembled unitary fuse structures disclosed by Lohausen as specific embodiments of his invention, are basically sound and satisfactory for certain purposes, but have one disadvantage from the standpoint of present common practice. This is that the fusible elements are not practically and readily replaceable, so that, after operation, a fuse device such as disclosed by Lohausen would have to be discarded or returned to the factory to be refused.

It is one of the objects of my present invention to overcome this disadvantage by provision of a multiple element fuse link suitable for the practice of the Lohausen invention and employable as a replacement or refill unit in an expulsion fuse holder. This feature of my invention, in its broader aspects, resides in provision of a unitary fuse link having a plurality of fusible elements together with means arranged to define, in the expulsion bore of an enclosing fuse holder, a plurality of relatively small cross-section arcing chambers or compartments, each individual to a respective one of the fusible elements, and the walls of which chambers or compartments are designed to yield upon interruption of excess current of large magnitude'so as to afford enlargement of the gas expansion space.

Other features, comprising other objectives of my invention, reside in the provision of detailed refinements such as tensioning means for the fusible elements of the multiple element fuse link and improvements in the'terminal and connection means of the fuse link.

A more complete understanding of these and other objectives, as well as of the details of that which I consider to be novel and my invention, will be secured from the following description and the appended claims, taken in conjunction with the accompanying drawing wherein Fig. 1 shows a longitudinal section of an exemplary form of expulsion-fuse device embodying the invention; Fig. 2 shows a transverse section taken along the line 2-2 of Fig. l; and Fig. 3 shows a modified arrangement of the tensioning means.

The enclosing casing or holder of the illustrated. fuse device comprises an insulating expulsion tube l0 which is open at one end and which has, at the other end, a, metallic terminal ferrule Ii and a metallic closure cap '12. A unitary fuse link, comprising an embodiment of the present invention, is removably disposed within this holder. The fuse link includes a plurality of current interrupting elements having a common terminal part I3. In the exemplary form illustrated, the terminal part is of the buttonhead type, having a. contact flange l4 which is clamped between cap I! and an inwardly extending mass or shoulder II on ferrule II. The illustratedfuselinkhasthreeparallelconnected current interrupting elements, although two. or more than three, may be employed, depending upon the current rating for which the fuse link is designed. Each current interrupting element has a fusible section which, in the embodiment illustrated, comprises a wire ll, although other forms of fusible section may be employed if desired. A flexible stranded conductor I1 is joined to one end of each of'the fusible wires by suitable means, such as a czimped sleeve indicated at 20. The other end of each of the fusible wires is joined in a suitable manner, as by crimping or soldering. to a respective one of a plurality of connection heads or shanks it formed integrally with terminal part It. The fusible section It and a portion of the conductor ll. of each of the interrupting elements, are surrounded by a separate one of a plurality of small bore insulating tubes 22. Conductors I'I extend out of the lower ends of these tubes and are joined. by braiding, into a slnsle cable extension 23 of sufficient length to extend out of the expulsion end of tube II for connection purposes. Alternatively. there may be employed a single stranded ingspringll. malcurrentintemiptiontakes connection conductor of the proper size and r length, and the strands of such conductor may be unbraided for a distance sumcient to provide the three individual conductors II.

In some cases, particularly with fuse links designed for higher current ratings, it may be found that the quick burning back of the fusible sections may be depended upon to effect proper interruption of slight overload currents. However, particularly for fuse links designed for lower current ratings, it is desirable to provide some form of fuse link tensioning means to insure rupture of the fusible sections on extremely low currents. This is accomplished in the embodiment of Fig. l, by the employment of a plurality of tension springs 24, each individual to a respective one of the tubes 22 and in surrounding relation to a portion of the corresponding conductor ll. Each of these springs is connected at one end to a respective one of the sleeves 20, and the other ends of the springs have enlargements 25 which bear against the ends of the respective tubes 22. Inthe alternative modification of Fig. 3, there is employed a single compression spring 28 which surrounds all of the conductors l1 exteriorly of the ends of tube 22. One end of spring 28 is made sufficiently large to bear against the ends of all of the tubes 22, while the other end of thisspring is joined to a sleeve 21 secured on extension cable 23. To insure proper positioning of tubes 22, the upper ends of these tubes are provided with metallic eyelets Ill which bear against shoulders ti on shanks 2i so as to oppose th force of the tensioning spring or springs.

Upon subjection of one of the described fuse links to excess current of relatively small magnitude, the fusible sections thereof attain melting temperature and rupture successively, or in cascade, due to unavoidable irregularities in the characteristics of the different conductors. In the case of the embodiment shown in Fig. l, the ends of the fusible section which ruptures first, are rapidly separated by the corresponding one of the springs 24. Thereupon, the remaining fusible sections are subjected to the whole current until the second fusible section ruptures and place when the last remaining fusible section rupturesanditsendsareseparatedtherequired distance. In some cases, where the excess current is'of extremely small magnitude, the final interruption may take place primarily due to separation of the ends of all of the ruptured sections by their tensioning prings and without the necessity for expulsion action. However, upon interruption of excess current which. though small. is of appreciable magnitude, there is produced upon rupture of the last remaining fusible section. an expulsion action which is sumcicnt to expel conductors ii and extension 28 from theendoftube llsoastoaidinthecurrent interruption.

The low current operation of the modification ofl'ig.3issimilartothatjustdescribed,with the exception that the fusible sections which rupture prior to the final section are burned back so that the gaps are produced relatively more'slowly, and the single tensioning spring 2! becomes effective to produce rapid separation ofthe endsofallofthesectionsonlyafternmture of the final section. If the tensioning means is dispensed with, the low current operation is similar to that ducribed in the previously referred to Iohausen patent in that, following rupture of the last remaining fusible section, there may occura transfer or restriking ofthe arc across one or more of the gaps produced by ruptureandburningbackofprecedingonesof its ends are rapidly separated by its correspondthe fusible sections. This transfer or restriking of the arc may continue until the ends of all of the ruptured sections are separated sufficiently to efiect total interruption of the current. It will be understood. of course. that the described operation in each case takes place in a very short period of time.

Due to the progressive rupture of the fusible sections and the small bores of the individual tubes 22, the described constructions have the important advantage, upon interruption of excess current of relatively small magnitude, that the final current interruption takes place in a restricted space wherein there may be developed considerably higher and more effective expulsion pressures than could be developed in a large expulsion bore, such as that of tube Ill, designed for proper interruption of large magnitude excess current. 1

Upon subjection of a fuse link structure as herein described, to excess current of large magnitude, such as short circuit current, all of the fusible sectons melt and rupture approximately simultaneously and considerable pressure is developed in tubes 22. These tubes are designed so that the walls of one, several, or all of the tubes yield or rupture when the pressure exceeds a predetermined magnitude. The resultant effective enlargement of the gas expansion space permits the arc gases to expand in a space which is greater than that normally provided by tubes 22. and which expansion space may attain substantially to the magnitude of the main expulsion bore of tube It. Thus. upon heavy current interruption there is provided sufficient expulsion pressure to effect proper arc extinction without the pressure exceeding safe and controllable limits.

From the foregoing it will be seen that a fuse embodying the present invention is capable of operating as a small bore expulsion fuse for interruption of excess current of small magnitude and as a large bore expulsion fuse for interruption of excess current of large magnitude. Various combinations of the previously described operations take place to greater or less extent for interruption of currents intermediate the extremely small excess currents and the currents.

of large magnitude. Thus satisfactory operation is insured over a wide range of current magnitude.

The present invention is not limited to the particular details of construction of the exemplary embodiments illustrated, and I contemplate that various modifications will suggest themselves to those skilled in the art. Hence, I wish it to be understood that I desire to cover by the appended claims such other modifications as do not depart from the true spirit and scope of the present invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In an electric fuse including a fuse holder of the expulsion type, a unitary buttonhead fuse link removably disposed in said holder and comprising a plurality of current interrupting elements in parallel relationship and a plurality of relatively small .bore insulating tubes, each of which tubes extends in surrounding relation to a portion of a respective one of said interrupting elements, which said portion of each of said interrupting elements includes a fusible section; said tubes being designed to withstand pressure incident to interruptieii of excess current of redetermined relatively small magnitude; said tubes being designed to yield, so as to afford communication between the spaces interiorly of the tubes and the surrounding space in said holder, upon development of high pressure incident to interruption of excess current of predetermined relatively large magnitude.

2. A unitary fuse link for installation in a fuse holder of the expulsion type; said fuse link comprising a buttonhead terminal element, a plurality of current interrupting elements, each of which last mentioned elements includes a fusible conductor and a connection conductor connected with one end of said fusible conductor, means connecting the other end of each of said fusible conductors with said terminal element, and a plurality of relatively small bore expulsion tubes, each of which tubes extends in surrounding relation to a portion, including the fusible conductor, of a respective one of said interrupting elements, said connection conductors extending out of said tubes for connection purposes exteriorly of the tubes,

3. A unitary fuse link for installation in a fuse holder of the expulsion type; said fuse link comprising a terminal member, a plurality of relatively small bore insulating tubes, a plurality of fusible elements disposed each in a respective one of said tubes and each having one and connected with said terminal member, and a plurality of relatively long conductors connected each with the other end of a respective one of said fusible elements, each of said conductors having a flexible portion of substantial length extending outside of the corresponding one of said tubes 50' as to be employable for connection purposes exteriorly of a fuse holde in which said fuse link is installed.

4. A unitary fuse link for installation in a fuse holder of the expulsion type; said fuse link comprising a terminal member, a plurality of relatively small bore insulating tubes, a plurality of fusible elements disposed each in a respective one of said tubes and each having one end connected with said terminal member, a plurality of conductors connected each with the other end of a respective one of said fusible elements, and means providing a single flexible connection conductor joined with said plurality of conductors outside of said tubes and having suflicient length to be employable for connection purposes exteriorly of a fuse holder in which said fuse link is installed.

5. A unitary fuse link comprising a plurality of insulating tubes'extendin in substantially parallel juxtaposition, a plurality of fusible elements disposed each in a respective one of said tubes, 9. terminal member adjacent one end of said tubes and connected with one end of each of said fusible elements, and a plurality of relatively long stranded conductors connected each with the other end of a respective one of said fusible elements, each of said conductors having a portion extending out of the end of the corresponding one of said tubes opposite to said first mentioned end of the tubes, saidoutwardly extending portions of the conductors being joined exteriorly of the tubes so as to provide a single flexible connection conductor of substantial length.

6. A unitary fuse link comprising a plurality of insulating tubes extending in substantially parallel juxtaposition, a terminal member adjacent one end of said tubes and having a plurality of connection heads, a plurality of fusible elements disposed each in a respective one of said tubes and each having one end connected with a respective one of said connection heads, and a plurality of conductors connected each to the other end of a respective one of said fusible elements, said conductors having flexible portions extending exteriorly of the ends of said tubes opposite to said first mentioned end for connection purposes.

7. In an expulsion fuse device including an insulating tubular fuse holder having a terminal adjacent one end and/designed for expulsion of gases at the other end; a'unitary fuse link removably disposed in said holder and comprising elements disposed each in a separate one of said compartments and each having one end connected with said terminal part, and a plurality of conductors connected each with the other end of a respective one of said fusible elements, said conductors having flexible portions extending exteriorly'of said compartments adjacent said other end of said holder for connection purposes.

8. A'unitary fuse link for installation in a fuse holder having a hollow terminal adjacent one end and designed for expulsion of gases at the other end; said fuse link comprising a terminal part having a contact flange for engagement with a hollow fuse holder terminal, a plurality of relatively small bore insulating tubes, a plurality of fusible elements each disposed in a respective one of said tubes and each having one and connected with a separate connection head on said terminal part, a plurality of conductors connected each to the other end of a respective one of said fusible elements, said conductors having flexible portions extending exteriorly of said tubes, and means providing a single flexible connection conductor joined with said portions of said plurality of conductors and having suflicient length to extend out of the expulsion end of an enclosing fuse holder ior connection purposes.

9. A unitary iuse link for installation in a fuse holder oi the expulsion type; said iuse link comprising a plurality of current interrupting elements connected in parallel relationship, a plurality or relatively small bore expulsion tubes extending each in surrounding relation to a portion of a respective one of said interrupting elements; which said portion of each or said interrupting elements includes a fusible section. and spring means connected for tensioning said interrupting elements.

10. A unitary fuse link ior installation in a fuse holder of the expulsion type; said fuse link comprising a terminal element, a plurality of current interrupting elements. each oi which last mentioned elements includes a i'usible conductor and a connection conductor connected with one end of said fusible conductor, means connecting the other end or each oi said iusibie conductors with said terminal element, a plurality of relatlveiy small bore expulsion tubes, each of which tubes extends in surrounding relation to a portion, including the fusible conductor, of a respective one or said interrupting elements. said connection conductors extending out of said tubes for connection purposes extericrly oi. the tubes. and a plurality of springs each connected to tension a respective one 0! said interrupting ele- 15 ments.

GEORGE I". LINCKS. 

